§3.1A · Under Visual examination
Weld porosity: what the CWI wants you to name and judge
Weld porosity is gas that got caught in the weld and left holes behind: pinholes you can see on the cap, pockets you'll only find on film. For the CWI you need three things: the A3.0 name for the pattern in front of you, the likely cause, and the knowledge that only the governing code decides whether it passes.
- Exam
- CWI
- Clause
- §3.1A
- Tags here
- 7
- Parent
- Visual examination
3.1A.1Three ways gas gets in
Gas gets into the puddle three ways, whichever of the joining processes you use: the shielding fails, the joint is dirty, or something brings in moisture.
- Lost shielding: wind across the job, gas flow set wrong, a nozzle packed with spatter, a leaking hose or fitting.
- Contamination: oil, paint, primer, heavy rust or scale in the joint.
- Moisture: low-hydrogen electrodes left out of the oven, damp flux, condensation on cold plate.
By process
Self-shielded flux-cored wire makes its shielding from the core, so wind bothers it less, but electrical stickout and voltage matter more. FCAW-S vs FCAW-G covers the difference. Aluminum is touchy: hydrogen from moisture, oxide and dirty filler wire shows up as porosity on GTAW and GMAW alike, which is why aluminum prep is fussier than steel prep.
What you can and can't see
Visual inspection only finds pores that break the surface. A clean cap can sit on top of buried porosity. On a radiograph a pore is less metal, so it reads darker than the weld around it, which is why RT is the method that finds volumetric flaws best. RT vs UT explains the split, and visual examination is the parent clause.
3.1A.2The A3.0 names
- Scattered porosity
- Pores spread through a single pass or across several passes, with no pattern. Older texts call it uniformly scattered.
- Cluster porosity
- A tight local group of pores, often at an arc start or stop.
- Linear porosity
- Pores lined up along a fusion boundary, the root, or the line between two beads.
- Elongated porosity
- Pores clearly longer than they are wide.
- Piping porosity
- Elongated porosity whose length points through the weld rather than along it. Shop slang: wormholes.
3.1A.3From cause to fix
| Cause | Where it shows | What to check | Most exposed |
|---|---|---|---|
| Wind or drafts | Outdoor work, open bay doors | Screens, gas flow, nozzle condition | GMAW, FCAW-G, GTAW |
| Damp electrodes or flux | Whole runs, worst at starts | Oven storage, time out of the oven | SMAW low-hydrogen, SAW |
| Dirty joint | Along the joint | Cleaning before welding: oil, paint, primer, rust | Every process |
| Long arc or wrong stickout | On and off along the run | Arc length, stickout against the WPS | SMAW, FCAW-S |
| Oxide and moisture on aluminum | Aluminum welds | Fresh oxide removal, clean dry filler | GTAW, GMAW |
3.1A.4Name it, cause it, size it
Pore patterns, their causes, and what goes on the report.
0 of 7 tagged · 0 accepted
Tag 01
Porosity in welding is best characterized by which of the following descriptions?
Remarks on every option
- A Uneven surface from cooling isn't porosity. Porosity is gas cavities.
- B Correct: Moisture, dirt or lost shielding puts gas in the puddle. If it can't rise out before the metal freezes, it stays behind as voids.
- C That's incomplete joint penetration: a lack of depth, not gas.
- D That's a crack: a fracture, not a gas pocket.
Pick an option. The remarks on all 4 open here.
Tag 02
How should an inspector evaluate the acceptability of scattered porosity?
Remarks on every option
- A A count alone isn't how acceptance criteria are written. Size and spacing matter too.
- B The largest pore is one input. Criteria also limit totals and spacing.
- C Correct: Measure pore sizes and how they're spaced along the weld, then judge them against the governing code's acceptance criteria.
- D Eyeballing it gives you no numbers to judge against.
Pick an option. The remarks on all 4 open here.
Tag 03
What causes porosity in GMAW welds?
Remarks on every option
- A Correct: When gas doesn't cover the puddle (drafts, low flow, a clogged nozzle), air gets in and leaves gas pockets.
- B Wrong wire size causes other trouble, but it isn't the main cause of porosity.
- C High voltage makes a long arc that can pull in some air, but the main cause is poor gas coverage.
- D Slow travel tends to cause overlap or too much heat, not porosity.
Pick an option. The remarks on all 4 open here.
Tag 04
A welder completes a job and notices a defect in the weld. The defect is described as a series of elongated cavities aligned parallel to the weld face. What type of discontinuity is likely present?
Remarks on every option
- A Incomplete fusion is an unfused interface, not gas cavities.
- B Correct: Elongated cavities lying along the weld are elongated porosity: gas pockets stretched out as the weld froze.
- C Overlap is unfused weld metal on the plate surface at the toe, not cavities.
- D Undercut is a groove at the toe, not a cavity in the weld.
Pick an option. The remarks on all 4 open here.
Tag 05
How should an inspector document the location of clustered porosity in a long seam weld?
Remarks on every option
- A A general note isn't enough to find it again on a long seam.
- B 'Approximately' won't get the repair crew to the right spot.
- C Correct: Measure from a fixed reference point (weld start or a datum mark) and record how long the cluster runs, so it can be found and judged.
- D A pore count without a location doesn't tell anyone where to look.
Pick an option. The remarks on all 4 open here.
Tag 06
A macroetch of a fillet weld shows several elongated gas cavities running from near the root up toward the weld face, roughly perpendicular to the surface. Which porosity form is this?
Remarks on every option
- A Cluster porosity is a localized group of pores. It describes grouping, not long tubes running up through the weld.
- B Linear porosity is pores lined up in a row, usually along a fusion line or the root. These cavities each run across the weld instead.
- C Scattered porosity is pores spread through the weld with no pattern. It says nothing about a long, tubular shape.
- D Correct: Piping porosity (wormholes) is elongated porosity whose long dimension lies roughly perpendicular to the weld face, as in this etch.
Pick an option. The remarks on all 4 open here.
Tag 07
On a radiograph of a multipass butt weld you see small dark spots with smooth, round outlines, and near them a dark shape with ragged edges and uneven width lying between two passes. How do you read them?
Remarks on every option
- A Porosity and slag both image dark because they're less dense than the steel around them. A light spot means denser material, such as tungsten.
- B Correct: Gas pores show as rounded dark spots with smooth outlines. Slag trapped between passes is also dark but irregular, with ragged edges.
- C This swaps the shapes. Slag is irregular and angular; gas pores come out round.
- D A pore images as a rounded spot whatever its size. A ragged, uneven shape between passes points to trapped slag, not a bigger pore.
Pick an option. The remarks on all 4 open here.
3.1A.5Porosity on the job
What's a pinhole in a weld?
Shop word for a small pore that breaks the surface. A pinhole on the cap can be the top of a pipe running down into the weld, so don't assume it's shallow.
Why is porosity so common in aluminum welds?
Hydrogen. Molten aluminum takes up far more of it than solid aluminum can hold, so it comes out as the weld freezes. Moisture, the oxide layer, oily wire and damp gas lines all feed it, which is why cleaning and dry filler matter more than on steel.
Is porosity always a defect?
No. It's a discontinuity, and codes allow limited porosity depending on weld type and loading. It becomes a defect only past those limits: see discontinuity vs defect.
Can surface porosity just be ground out?
Only within the repair rules of the governing code. Pores can run deeper than they look, so grind until it's sound, reweld if the section is now undersize, and inspect the area again to the same criteria.
Between jobs, not between books
Our CWI prep app puts practice questions on your iPhone or iPad for the gaps in a shift.